Frontier has facilitated $1.75 million of carbon removal purchases from Karbonetiq (United States), Limenet (Italy), and pHathom (Canada) on behalf of buyers Stripe, Shopify, and Google. Frontier buyers are the first customers for two out of three companies.
Frontier’s prepurchase program supports early-stage companies piloting new carbon removal solutions by buying their early tons. Companies in this round accelerate the development of two promising yet underexplored approaches (among the high-potential approaches previously identified by Frontier):
Ocean alkalinity enhancement (OAE) refers to a broad set of approaches aiming to increase the alkalinity of surface waters, boosting the ocean’s natural ability to absorb CO₂ and store it as bicarbonate. One specific method, ocean liming, uses high-purity, fast-dissolving minerals like hydrated quicklime, which is produced by heating widely available limestone. Studies suggest large-scale ocean liming could remove several billion tons of CO₂ annually, though producing low-carbon quicklime remains a key bottleneck. As an added benefit, OAE reverses ocean acidification locally, improving conditions for coral reefs and shellfish.
Surficial mineralization accelerates the natural reaction between atmospheric CO₂ and alkaline minerals found in rocks (e.g., ultramafic mine tailings) or industrial residues (e.g., steel and nickel slags). Crushing or grinding these materials exposes fresh, reactive surfaces, compressing the reaction process from geologic timescales to years or decades. As an added benefit, some mineralization approaches can help clean up mine waste or recover additional critical metals needed for the energy transition. The approach could, in principle, deliver over a billion tons of carbon removal annually. But scaling it depends on keeping the energy use and emissions from producing, transporting, and milling the feedstocks low enough to make it effective and affordable.
Meet the projects
Mineralization | Santa Barbara, CA, US | 2,142 tons
Karbonetiq takes alkaline industrial residues that naturally absorb CO₂ from the air, then processes and cycles them through a low-cost, passive aeration system. The company then uses sensors and software to measure how much carbon is captured. Karbonetiq’s process could significantly improve mineralization rates and reduce the land required for deployment, allowing projects to be co-located with existing industrial activities.
Ocean alkalinity enhancement | Lecco, Italy | 330 tons
Limenet is developing a custom electric kiln to produce zero-carbon quicklime—a clean, fast-reacting feedstock that can be mineralized on land or used for OAE. Limenet's carbon-free quicklime enables a range of promising approaches to scale, including surficial mineralization, ocean liming, and mineral looping DAC. It can also support broader decarbonization efforts by replacing industrial quicklime commonly used in applications like steel production and cement manufacturing.
Ocean alkalinity enhancement | Nova Scotia, CA | 510 tons
pHathom captures CO₂ emissions from coastal bioenergy plants using a slurry of limestone, seawater, and biocatalysts inside a weathering reactor, forming a stable bicarbonate solution that can be safely discharged into the ocean. Their approach provides a critical storage solution for coastal projects across bioenergy with carbon capture and storage (BECCS), direct air capture (DAC), and industrial carbon capture and storage (CCS), enabling scalability where geologic injection is not feasible. Their biocatalyst could facilitate the wider use of limestone for other carbon removal approaches, including field weathering and inland water alkalinity enhancement.
Be part of our next purchases
If you are a carbon removal supplier, we’d love to hear from you. You can find more details about Frontier’s purchase process here.
If you are interested in becoming a buyer of carbon removal through Frontier, please get in touch at buyers@frontierclimate.com.